Such a sample carrier is known from the catalog of the firm Structure Probe, Inc., with an address at 569 East Gay Street, West Chester, PA 19380, USA, under catalog number 2020C-XA, as described on the priority date of the present patent application on the website http://www.2spi.com/catalog/grids/square_mesh—200.shtml. The described embodiment concerns a round copper foil, whereby the circular middle portion is perforated with square openings. The square openings have dimensions of 90×90 μm2 and are separated from one another by bars with a width of 35 μm. The middle portion is surrounded in its entirety by an edge portion without openings and with a width of 0.225 mm. The external diameter of the sample carrier is 3.05 mm and its thickness is approximately 20 μm. As a result of the openings, the middle portion is partially transparent to electrons, which can pass through the openings but not through the copper bars. The edge portion, which contains no openings, contains a substantial portion of the material of the sample carrier, and thus contributes substantially to the stiffness and strength of the sample carrier, thereby having a strengthening effect.
Such sample carriers are available in other materials, such as gold, nickel and plastic, and also in materials with a coating, such as gilded copper. Such sample carriers are also available with middle portions of another form, e.g. with other dimensions of the openings and/or bars. The thickness of these sample carriers is usually of the order of magnitude of 5 to 50 μm, and is uniform across the entire sample carrier. The thickness of sample carriers is important in the sense that the middle portion should remain at least partially transparent to electrons when the sample carrier is tilted. Tilting of the sample carrier has, after all, the effect that the electron beam does not impinge perpendicularly on the middle portion of the sample carrier. In the case of the stated dimensions of the openings, and in the case of a thin sample carrier, it will be possible to achieve a larger tilt of the sample carrier—before the transparency becomes unacceptably small—than in the case of a thick sample carrier. For a given maximal tilt and a given dimension of the opening, the maximal thickness of the sample carrier is thus determined. Tilting the sample carrier up to an angle of, for example, 70 degrees is desirable in the case of various types of analysis, such as in the case of tomography for the purpose of a three-dimensional reconstruction of a sample volume.
The user of such a sample carrier will attach a sample to said middle portion of the sample carrier in a manner known per se, and, eventually, will mount the sample carrier with sample on a sample holder of a Transmission Electron Microscope, also referred to as a TEM. Manipulation of the sample carrier usually occurs in this process using pincers. Manipulation of the sample carrier demands much experience, in view of the exceptionally small thickness of the sample carrier. Even for an experienced person, there is a real chance that the sample carrier and/or the sample attached thereto will be deformed or damaged. Greater stiffness and strength of the sample carrier are desired, and can be attained by using a thicker sample carrier; however, this is at odds with the desire to maintain a thin sample carrier for the purpose of analyses in which tilting of the sample carrier is of importance, such as in the case of tomography. In addition, if the pincers touch the middle portion of the sample carrier, the sample mounted thereto can be damaged.
After the sample carrier has been mounted to the sample holder of the TEM, this sample holder can be introduced into the TEM. Once the sample has been introduced, it can be analyzed in a fully automatic manner with the aid of a known program such as “Leginon” from the AMI group of the Scripps Research Institute. Another possibility is that, after the sample has been introduced into the TEM, the TEM is operated via telecommunication—such as via internet—by a user somewhere else, whereby, for example, this user hires analysis time from the administrator of the TEM.
There is a desire to maintain transparency in the middle portion of the sample holder in the case of large tilt angles, so that the sample can be analyzed using, for example, tomography. There is also a desire to realize automatic introduction and removal of sample carriers in a TEM, seeing as this would make it possible to use the TEM continuously without human intervention. In the case of such introduction and removal of sample carriers, there is, in view of the fragile nature of the thin sample carriers, the possibility of deformation of and/or damage to the sample carriers and the samples attached thereto.